When the DRM scheduler times out, it's possible that the GPU isn't hung;
instead, a job may still be running, and there may be no valid reason to
reset the hardware. This can occur in two situations:
1. The GPU exposes some mechanism that ensures the GPU is still making
progress. By checking this mechanism, the driver can safely skip the
reset, re-arm the timeout, and allow the job to continue running until
completion. This is the case for v3d, Etnaviv, and Xe.
2. Timeout has fired before the free-job worker. Consequently, the
scheduler calls `sched->ops->timedout_job()` for a job that isn't
timed out.
These two scenarios are problematic because the job was removed from the
`sched->pending_list` before calling `sched->ops->timedout_job()`, which
means that when the job finishes, it won't be freed by the scheduler
though `sched->ops->free_job()` - leading to a memory leak.
To solve those problems, create a new `drm_gpu_sched_stat`, called
DRM_GPU_SCHED_STAT_NO_HANG, that allows a driver to skip the reset. The
new status will indicate that the job must be reinserted into the
pending list, and the hardware / driver will still complete that job.
Signed-off-by: Maíra Canal <mca...@igalia.com>
---
drivers/gpu/drm/scheduler/sched_main.c | 43 ++++++++++++++++++++++++++++++++--
include/drm/gpu_scheduler.h | 3 +++
2 files changed, 44 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index
0f32e2cb43d6af294408968a970990f9f5c47bee..d3f48526883cc7ceea0cd1d0c62fb119f7092704
100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -374,11 +374,16 @@ static void drm_sched_run_free_queue(struct
drm_gpu_scheduler *sched)
{
struct drm_sched_job *job;
- spin_lock(&sched->job_list_lock);
job = list_first_entry_or_null(&sched->pending_list,
struct drm_sched_job, list);
if (job && dma_fence_is_signaled(&job->s_fence->finished))
__drm_sched_run_free_queue(sched);
+}
+
+static void drm_sched_run_free_queue_unlocked(struct drm_gpu_scheduler *sched)
+{
+ spin_lock(&sched->job_list_lock);
+ drm_sched_run_free_queue(sched);
spin_unlock(&sched->job_list_lock);
}
@@ -531,6 +536,31 @@ static void drm_sched_job_begin(struct drm_sched_job
*s_job)
spin_unlock(&sched->job_list_lock);
}
+/**
+ * drm_sched_job_reinsert_on_false_timeout - reinsert the job on a false
timeout
+ * @sched: scheduler instance
+ * @job: job to be reinserted on the pending list
+ *
+ * In the case of a "false timeout" - when a timeout occurs but the GPU isn't
+ * hung and the job is making progress, the scheduler must reinsert the job
back
+ * into the pending list. Otherwise, the job and its resources won't be freed
+ * through the &drm_sched_backend_ops.free_job callback.
+ *
+ * Note that after reinserting the job, the scheduler enqueues the free-job
+ * work again if ready. Otherwise, a signaled job could be added to the pending
+ * list, but never freed.
+ *
+ * This function must be used in "false timeout" cases only.
+ */
+static void drm_sched_job_reinsert_on_false_timeout(struct drm_gpu_scheduler
*sched,
+ struct drm_sched_job *job)
+{
+ spin_lock(&sched->job_list_lock);
+ list_add(&job->list, &sched->pending_list);
+ drm_sched_run_free_queue(sched);
+ spin_unlock(&sched->job_list_lock);
+}
+
static void drm_sched_job_timedout(struct work_struct *work)
{
struct drm_gpu_scheduler *sched;
@@ -564,6 +594,9 @@ static void drm_sched_job_timedout(struct work_struct *work)
job->sched->ops->free_job(job);
sched->free_guilty = false;
}
+
+ if (status == DRM_GPU_SCHED_STAT_NO_HANG)
+ drm_sched_job_reinsert_on_false_timeout(sched, job);
} else {
spin_unlock(&sched->job_list_lock);
}
@@ -586,6 +619,9 @@ static void drm_sched_job_timedout(struct work_struct *work)
* This function is typically used for reset recovery (see the docu of
* drm_sched_backend_ops.timedout_job() for details). Do not call it for
* scheduler teardown, i.e., before calling drm_sched_fini().
+ *
+ * As it's used for reset recovery, drm_sched_stop() shouldn't be called
+ * if the driver skipped the reset (DRM_GPU_SCHED_STAT_NO_HANG).
*/
void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
{
@@ -671,6 +707,9 @@ EXPORT_SYMBOL(drm_sched_stop);
* drm_sched_backend_ops.timedout_job() for details). Do not call it for
* scheduler startup. The scheduler itself is fully operational after
* drm_sched_init() succeeded.
+ *
+ * As it's used for reset recovery, drm_sched_start() shouldn't be called
+ * if the driver skipped the reset (DRM_GPU_SCHED_STAT_NO_HANG).
*/
void drm_sched_start(struct drm_gpu_scheduler *sched, int errno)
{
@@ -1192,7 +1231,7 @@ static void drm_sched_free_job_work(struct work_struct *w)
if (job)
sched->ops->free_job(job);
- drm_sched_run_free_queue(sched);
+ drm_sched_run_free_queue_unlocked(sched);
drm_sched_run_job_queue(sched);
}
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index
83e5c00d8dd9a83ab20547a93d6fc572de97616e..257d21d8d1d2c4f035d6d4882e159de59b263c76
100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -393,11 +393,14 @@ struct drm_sched_job {
* @DRM_GPU_SCHED_STAT_NONE: Reserved. Do not use.
* @DRM_GPU_SCHED_STAT_RESET: The GPU hung and successfully reset.
* @DRM_GPU_SCHED_STAT_ENODEV: Error: Device is not available anymore.
+ * @DRM_GPU_SCHED_STAT_NO_HANG: Contrary to scheduler's assumption, the GPU
+ * did not hang and is still running.
*/
enum drm_gpu_sched_stat {
DRM_GPU_SCHED_STAT_NONE,
DRM_GPU_SCHED_STAT_RESET,
DRM_GPU_SCHED_STAT_ENODEV,
+ DRM_GPU_SCHED_STAT_NO_HANG,
};
/**
--
2.50.0
